The Asia-Pacific region experiences some of the world's most violent natural hazards, being exposed to earthquakes, volcanic eruptions, cyclones and monsoons. It is also home to many of the world's most populous megacities with large exposures to hazards. Indeed, government statistics reveal an annual average of 2.7 disasters a day in Indonesia alone. This high risk of natural disasters in developing nations has considerable implications for international aid programs, as disasters significantly compromise the achievement of development goals and the effectiveness of aid investments. Recognising this issue, AusAID requested Geoscience Australia to conduct a broad natural hazard risk assessment of the Asia-Pacific region. This assessment included earthquake, volcanic eruption, tsunami, cyclone, flood, landslide and wildfire hazards. A crucial aspect in the assessment of natural hazard risk is the metric used to define a past disaster and therefore the risk of future disasters. For this preliminary study, we used "significantly impacted population" as the risk metric. This deliberately vague metric is intended to capture the potential for human death, injury, and displacement, as well as prolonged loss of access to essential services and/or shelter, and/or significant damage to agriculture, horticulture and industry such that external assistance is required. However, future work in the Asia-Pacific region will need to be able to determine these vulnerabilities more accurately, considering, for example, the vulnerabilities of buildings and infrastructure in relation to building codes and construction practice, economic cost, and the spatial variability of the intensity of different hazard events. For this study, we determined the frequencies and magnitudes of a range of sudden-onset natural hazards and evaluated the potential disaster impact. Extra emphasis was placed on relatively rare but high impact events that may not be well reflected in the historical record, such as the 2004 Indian Ocean tsunami. We concluded that the potential is high for a natural disaster to seriously affect more than one million people in the Asia-Pacific region, with specific risks as follows: - Megacities in the Himalayan Belt, China, Indonesia and the Philippines are prime candidates for a million-fatality earthquake. - Hundreds of thousands may be seriously affected by volcanic disasters at least once a decade in Indonesia and once every few decades in the Philippines. - The population explosion in the mega-deltas of Asia (e.g., Bangladesh), combined with increasing vulnerability to climate change, indicates that a tsunami, flood or cyclone event significantly impacting tens of millions is likely. - Finally, many Pacific Island nations have a high potential for catastrophic disasters that may significantly impact large proportions of their populations, disasters that are most likely to overwhelm a local and national governments-response and recovery capacity.

The aim of this document is to provide the Attorney General's Department (AGD) with an assessment of the nearshore tsunami hazard for Australia. This assessment is one of the tsunami capacity building initiatives of the AGD to support the tsunami planning and preparation initiatives of the States and Territories. It follows the national deep water probabilistic tsunami hazard assessment completed in 2008 [1] that showed that Western Australia has the highest offshore hazard, the east coast of Australia has a moderate offshore hazard, while the smallest hazard can be found off Australia's southern coast. The intent of this nearshore assessment is to add interpretative value to the deep water assessment by estimating the amplification factor that can be applied to convert the deep water hazard to the nearshore tsunami hazard at a number of Australian communities. Further, the deep water assessment did not provide data for most of Victoria, Northern Territory, the west coast of Cape York Peninsula in Queensland, or the north coast of Tasmania due to the shallow water of the Gulf of Carpentaria, and the Torres and Bass Straits. Therefore, this nearshore assessment provides these areas with a tsunami hazard assessment for the first time

The report summarises earthquake and tsunami information worldwide in 1998 but with a focus on Australia for use by scientists, engineers and the public. Maps of the seismicity are presented on a state-by-state basis and isoseismal maps are included for the significant earthquakes.

The Joint Australian Tsunami Warning Centre (JATWC) was established in response to the Indian Ocean tsunami in 2004. The JATWC is a collaboration between Geoscince Australia and the Australian Bureau of Meteorology to provide tsunami warnings to the Australian public. This arcticle discusses the actions of the JATWC in response to the magnitude 7.4 earthquake that occurred south of New Zealand on the September 30, 2007. This earthquake generated a tsunami and a potential threat warning was issued for the Australian south east coast. The methods used to analyse the earthquake and the tsunami are examined as well as the future direction of operational capabilities in terms of tsunami modelling.

Most tsunami are caused by earthquakes that displace the water column by faulting the sea bottom or causing submarine landslides. Australia is surrounded by 8,000 km of active, earthquake-prone, plate margins. In Western Australia tsunami hazard is highest in the northwest facing the subduction zones of the Indonesian arc. Tsunami hazard along the eastern coast comes from subduction zones from the Solomon Islands in the northeast to the Puysegur Trench south of New Zealand. Images of the tsunami of 26 December 2004 impacting Thailand showed tsunami several metres high inundating large sections of shore line. Australia is much farther from the tsunami sources, and is more likely to face tsunami with smaller heights regionally but possibly increasing unpredictably to much larger heights locally. The Australian Government has funded the establishment of the Australian Tsunami Warning System (ATWS). End-to-end warning systems consider the development of mitigation strategies, monitoring for events, issuing warnings, and response and recovery phases after the event. The geosciences play important roles in several of these steps. Hazard mapping requires the study of the earthquake source regions (fault geometry, maximum likely earthquake magnitude and its probability, and estimates of the resulting tsunami height and direction). The development of mitigation strategies requires estimating the propagation of tsunami across the deep ocean, shoaling in the shallow waters near the shore line, the inundation of the land and the impact on people and infrastructure. The detection of earthquakes requires access to national and international seismograph networks that work interoperably in near-real-time, and algorithms for the rapid automatic determination of their locations (including depth), magnitudes and focal mechanisms. In cases where there are no sea level gauges between the source and coastline, the warning systems rely entirely on earthquake parameters. Published with the permission of the CEO of Geoscience Australia.

Palaeotsunami investigations can enhance our understanding of tsunami hazard in the Australian region, providing a means of assessing future risk. Previous researchers have suggested that at least six large tsunami impacted the NSW coast during the Holocene, some with run-up in excess of +100 m asl and inundation of 10 km inland. However, this evidence is contentious as it focuses on poorly understood rocky shoreline features and proposes tsunami signatures that have not been described in other parts of the world. If such evidence is substantiated, it has profound implications for the tsunami preparedness of the NSW communities. This study focuses on late Holocene coastal sedimentary records from backshore environments in NSW to develop an assessment of whether catastrophic marine inundation such as tsunami played a significant role in coastal evolution. The advantages of studying backshore environments are that a more continuous sedimentary record is likely to be preserved than on rocky shorelines and an estimate of tsunami recurrence can be obtained if several tsunamigenic units are found in sequence. Fifty cores from sixteen coastal water bodies in southern and central NSW were studied for evidence of past tsunami inundation. Potentially tsunamigenic sediment horizons were identified in some water bodies, which may be a result of localised submarine slump-induced palaeotsunami. However the small size and discontinuous distribution of these sedimentary units does not support the theory of "mega-tsunami" inundation. If such "mega-tsunami" had occurred, definitive evidence for them should be preserved on a wider scale in the backshore sedimentary record. This suggests that previous research for mega-tsunami on the NSW coastline needs to be re-evaluated.

The 2004 Sumatra-Andaman Earthquake and Indian Ocean Tsunami shattered the paradigm that guided our understanding of giant subduction zone earthquakes: that massive, magnitude 9+ earthquakes occur only in subduction zones experiencing rapid subduction of young oceanic lithosphere. Although this paradigm forms the basis of discussion of subduction zone earthquakes in earth sciences textbooks, the 2004 earthquake was the final blow in an accumulating body of evidence showing that it was simply an artefact of a sparse and biased dataset (Okal, 2008). This has led to the realization that the only factor known to limit the size of megathrust earthquakes is subduction zone length. This new appreciation of subduction zone earthquake potential has important implications for the southern Asia-Pacific region. This region is transected by many thousands of km of active subduction, including the Tonga-Kermadec, Sunda Arc, and the Makran Subduction zone along the northern margin of the Arabian Sea. Judging from length alone, all of these subduction zones are capable of hosting megathrust earthquakes of magnitude greater than 8.5, and most could host earthquakes as large as the 2004 Sumatra-Andaman earthquake (Mw=9.3). Such events are without historical precedent for many countries bordering the Indian and Pacific Oceans, many of which have large coastal populations immediately proximate to subduction zones. This talk will summarize the current state of knowledge, and lack thereof, of the tsunami hazard in the southern Asia-Pacific region. I will show that 'worst case' scenarios threaten many lives in large coastal communities, but that in most cases the uncertainty in these scenarios is close to 100%. Is the tsunami risk in SE Asia and the SW Pacific really this dire as the worst-case scenarios predict? The answer to this question relies on our ability to extend the record of tsunamis beyond the historical time frame using paleotsunami research.

A selection of images and short animations explaining key aspects of the 2004 Indian Ocean/ Sumatra tsunami, revised and issued for release to the media and other interested organisations on the tenth anniversary of the disaster. This selection updates existing resources previously released by Geoscience Australia.

The development of the Indian Ocean Tsunami Warning and mitigation System (IOTWS) has occurred rapidly over the past few years and there are now a number of centres that perform tsunami modelling within the Indian Ocean, both for risk assessment and for the provision of forecasts and warnings. The aim of this work is to determine to what extent event-specific tsunami forecasts from different numerical forecast systems differ. This will have implications for the inter-operability of the IOTWS. Forecasts from eight separate tsunami forecast systems are considered. Eight hypothetical earthquake scenarios within the Indian Ocean and ten output points at a range of depths were defined. Each forecast centre provided, where possible, time series of sea-level elevation for each of the scenarios at each location. Comparison of the resulting time series shows that the main details of the tsunami forecast, such as arrival times and characteristics of the leading waves are similar. However, there is considerable variability in the value of the maximum amplitude (hmax) for each event and on average, the standard deviation of hmax is approximately 70% of the mean. This variability is likely due to differences in the implementations of the forecast systems, such as different numerical models, specification of initial conditions, bathymetry datasets, etc. The results suggest that it is possible that tsunami forecasts and advisories from different centres for a particular event may conflict with each other. This represents the range of uncertainty that exists in the real-time situation.

The Mw=7.8 earthquake of 15 July, 2009 occurred along a section of the subduction zone south of New Zealand, where the Puysegur Block subducts beneath the Pacific Plate. The orientation of this subduction zone suggests that tsunamis generated along it pose a significant threat to the southeast coast of Australia, but since it had not experienced megathrust rupture until the 15 July event, the question of whether it was accumulating strain energy whose release could result in a large tsunami was open. We have used seismic, tsunami, geodetic and SAR data to study this earthquake and find that it involved primarily thrust motion on a fault plane dipping east at a shallow angle, consistent with expectations for a megathrust earthquake. The ability to use multiple data types to study this earthquake lead to improved ability to resolve parameters such as rupture velocity that are often difficult to constrain with seismic data alone. Seismic array data agree with rupture modelling of broadband waveforms in their prediction of a bilateral component to the earthquake rupture. Also, a tsunami of about 10 cm peak-to-peak amplitude was recorded by two tsunameter buoys in the Tasman Sea west of the epicenter, and we find that the tsunami travel times indicated by these data suggest the earthquake was characterised by a low rupture velocity of around 1 km/s. We will also present comparisons against GPS and InSAR data that further constrain parameters of the rupture. Finally, we will discuss the potential for earthquake activity further south along the Puysegur Trench, which poses a tsunami threat particularly to the eastern coast of Tasmania.